Comparative Study of MnO₂ and Fe₂O₃ Composites on Toona ciliata– Derived Carbon for Sustainable Supercapacitor Applications

Unmanaged wood waste, particularly in countries like Nepal, presents serious environmental concerns due to open burning and improper disposal, leading to carbon emissions, air pollution and land degradation. This study introduces an environmentally sustainable strategy to upcycle Toona ciliata wood scrap—an abundant and underutilized lignocellulosic biomass—into high performance carbon electrodes for green energy storage applications. Activated carbon (TCWAC) was synthesized via single-step pyrolytic carbonization followed by phosphoric acid activation, yielding a material with high specific surface area, hierarchical porosity, and excellent electrical conductivity. Electrochemical measurements using a three-electrode configuration in 6 M KOH revealed optimized potential windows of –1.0 to –0.2 V (TCWAC), –1.2 to 0 V (TCWAC–Mn), and –1.15 to –0.4 V (TCWAC–Fe). TCWAC exhibited a specific capacitance of 156.3 Fg⁻¹ at 1 Ag⁻¹, with an energy density of 3.5 Whkg⁻¹, and 80.2% capacity retention after 1000 charge–discharge cycles. Composites with MnO₂ and Fe₂O₃ were also evaluated. TWAC-Mn delivered 489.4 Fg⁻¹, 25.1 Whkg⁻¹, and 99.1% retention, whereas, TWAC-Fe achieved 321.3 Fg⁻¹, 6.3 Whkg⁻¹, and 90.3% retention. The superior performance of MnO₂ is attributed to its multiple oxidation states, facilitating reversible faradaic redox and enhanced pseudocapacitance. This work offers the first direct, systematic comparison of MnO₂ and Fe₂O₃ composites on a common biomass-carbon matrix under identical synthesis and testing conditions. The finding provides mechanistic insight into charge storage behaviour and demonstrate a scalable route for converting biomass waste into sustainable electrode materials, contributing to cleaner energy solutions and improved biomass valorization.